Qualitative analysis of Barium, Strontium, Calcium

During qualitative analysis of Barium, Strontium, Calcium, why do we use NH4CO3, NH4OH, NH4Cl. Even if we were to apply common ion effect, two NH4+ ions are enough right? What is the need for third one?

It might be there to completely describe what you might expect to find in your test tube after adding NH4OH or NH4CO3 [(NH4)2CO3? or (NH4)HCO3?] to your unknown which is probably a soluble chloride salt.